Mixing valves for a variety of applications have been known for many years. One application is that of controlling the temperature of a fluid in a fluid circulation system by combining the flow of the same fluid at different temperatures to provide the fluid at a desired temperature for use downstream thereof. Most frequently, this is accomplished by means of complicated valves having a number of moving parts.
In one application, a mixing valve is utilized in a space qualified thermal cooling system designed for use in space stations where it must serve as a temperature control bypass valve in a pumped fluid cooling loop. Because of the sensitivity of equipment to be cooled in such an environment, coupled with the extraordinarily expensive nature of such equipment and the difficulty of repair, the reliability of the thermal cooling system is a critical factor.
In practice, the failure of valves in space-related systems has been a serious problem. Conventional spool or poppet valves having numerous moving and sliding parts such as those disclosed in Cox U.S. Pat. No. 3,817,150, issued June 18, 1974, Bartholomans et al. U.S. Pat. No. 3,712,339, issued Jan. 23, 1973, and Baltus U.S. Pat. No. 3,.592,234, issued July 13, 1971, are all too complex to meet the stringent reliability requirements for space qualified thermal cooling systems since they can easily stick due to the close tolerances of the relatively movable parts and the fact that they do not have sufficient force to overcome any impediment to normal movement. Moreover, it has been found that conventional spool or poppet valves can wear over time leading to failure.
Among other attempts to provide valves for various applications and those disclosed in U.S. Pat. Nos. 4,005,733; 3,182,561; 2,775,254; and German Pat. No. 2,110,839.
While overcoming problems of this type, it is desirable to provide a mixing valve having a minimum of moving or sliding parts. It is also desirable to provide a mixing valve suitable for use in a thermal cooling system in the form of a utility cooling bus for use in space stations wherein individual pieces of equipment and experiments can be plugged into the thermal bus as needed. Further, it is desirable to provide a mixing valve having loose tolerances with balanced pressures, sufficient force to overcome sticking, and the ability to be repaired externally of the fluid cooling loop.
The present invention is directed to overcoming the above stated problems and accomplishing the stated objects.